The receptor with high affinity for IgE (FcERI) is found exclusively on mast cells, basophils and related cells. Aggregation of IgE occupied FcERI by antigen triggers both the release of preformed mediators such as histamine and serotonin, as well as stimulating the synthesis of leukotrienes. It is the release of these mediators which result in the allergic condition, The most thoroughly characterized FcERI is that of the rat basophilic leukemia (RBL) cell line. It consists of three different subunits: (1) A 40-50 Kilodalton (Kd) glycoprotein alpha chain which contains the binding site for IgE, (2) A single 33 Kd beta chain and (3) Two 7-9 Kd disulfide linked Gamma chains. The gene for human FcERI has never been completely cloned and isolated. Only the gene coding for the alpha subunit of rat FcERI has been cloned and sequenced [see Kinet, et al., Biochemistry, 26:4605 (1987)]. The instant invention encompasses the cloning, sequencing and expression of the alpha subunit of the human FcERI.